VarietySpeak for melodrama. Originally used in headlines in Variety magazine to save space (as the word has fewer, and narrower, letters).

Here's an example from November 16, 1966, (as a sub headline for a review):

"Night Train to Mundo Fine / Totally inept meller, grim b.o."
(Chad Gould, MST3K MOVIE GUIDE REVIEW Web site. <> (7 November 2002))
The term is still in use today in Variety:
"New CBS drama "The Agency" has done an OK job Thursdays opposite NBC's still-dominant "ER," with the CIA skein chipping away at the medical meller's advantage in male demos."
("Still Kicking," Variety, 4 February 2002. <> (7 November 2002))
And it has crept into plot summaries for video catalogs. Here's one for Las Vegas Shakedown, (1955):
"Dennis O'Keefe, Coleen Gray, Thomas Gomez and Robert Armstrong star in this crime meller."
(Movies Unlimited Product Page. <> (7 November 2002))